Fibre-reinforced composite moulding and manufacture thereof

ABSTRACT

Method of manufacturing a fibre-reinforced composite moulding, the method comrisinci the steps of: (a) disposing at least one layer of fibrous reinforcing material within a mould; (b) disDosing at least one pre-preg layer adjacent to the fibrous reinforcing material, the pre-preg layer comprising fibrous reinforcement at least partially impregnated with uncured first resin material, to form a laminar assembly of the at least one layer of fibrous reinforcing material and the at least one pre-preg layer within the mould; (c) applying a vacuum to the assembly; (d) infusing a flowable uncured second resin material, under the vacuum, into the at least one layer of fibrous reinforcing material: and (e) curing the first and second resin materials at least partially simultaneously to form the fibre-reinforced composite moulding which comprises at least one first structural portion formed from the fibrous reinforcement and the cured first resin material bonded to at least one second structural portion formed from the at least one layer of fibrous reinforcing material and the cured second resin material.

The present invention relates to a method of manufacturing afibre-reinforced composite moulding and to a fibre-reinforced compositemoulding. In particular, the present invention relates to afibre-reinforced composite moulding suitable for manufacturing largecomposite structures, such as turbine blades, bridges and boat hulls.

The three main thermoset composite processing methods currently used formanufacturing wind turbine blades are:

1. wet-laminating (also known as open moulding)—in this method, thethermoset resin can cure in ambient conditions, but the tools areusually heated to elevated temperature, 50-90° C., to speed up the resincuring process;2. the use of pre-preg materials, and the Applicant's own andpre-impregnated dry touch composite material sold under the product nameSPRINT®—such materials are typically cured at an elevated temperaturebetween 85° C. to 120° C.; and3. vacuum assisted resin transfer moulding (also known as VARTM, resininfusion, or vacuum infusion)—in this method liquid resin is infusedunder a vacuum into a dry fibre composite, and then can cure in ambientconditions, although the tools (i.e. the moulds) are usually heated toan elevated temperature between 50-90° C. to speed up the curingprocess.

The two main design concepts for a wind turbine are the structural sparconcept and the structural shell concept. In the structural spar concepta separate load carrying beam is made and bonded into two aerofoilsections. In the structural shell concept the two outer aerofoil shellsare manufactured containing the main structural fibre materials. Aseparate shear web is then used to provide the shear connection to formthe structural beam.

When using a wet-laminating or resin infusion (VARTM) processes it ismost common to use the structural shell design concept. The majority ofthe composite laminate is unidirectional (UD) to give the turbine itsflap-wise flexural rigidity. The remaining fibre materials are usuallystitched multiaxial products to provide shear reinforcement. Foam orwooden cores are also used to locally stiffen the blade sections. In themain structural beam portion the fibre reinforced laminate can be inexcess of 30 mm thick, and can reach a thickness of 80 mm in some of thelarger blades on the market, to give the necessary stiffness andstrength. In the main beam portion the UD material is interleaved atpoints with biaxial material to give the necessary shear strength,because in these thick sections transverse cracks would occur if it wasnot periodically reinforced in this manner.

When using ambient temperature curing resin systems, a significanttemperature rise can occur in these thick sections due to the exothermicheat generation of the curing process. To allow for this exotherm and beable to input heat to speed up the cure rate, a tool tolerant totemperatures of typically 90-130deg C. would typically be required. Thisincreases tool cost and complexity.

To make the unidirectional fibres handleable to apply into the mould,the UD fibres are supplied as a pre-made fabric which acts to hold thefibres together. This process adds cost and introduces waviness into thefibre which lowers its strength, particularly in compression. In thickcomposite sections, carbon fibre unidirectional fabrics have also provedto be difficult to reliably impregnate with a VARTM process. This ismainly due to the smaller diameter of carbon fibres leading to greatercompaction and lower permeability under vacuum.

The handling of high volumes of dry carbon fibre can lead to significantvolumes of small, loose, carbon fibre threads becoming airborne, throughthe wear and tear of handling the material, which is both hazardous tohealth and electrical equipment (as short circuits can inadvertently beestablished).

These factors make the use of uni-directional pre-pregs highlyattractive as the material can be correctly impregnated in the pre-pregmachine and made directly from low cost fibre rovings. The resin in thepre-preg holds the fibres together and in straight columns, maintaininggreater compressive modulus and strength. With a pre-preg machine it iseasier to isolate the dry fibre materials compactly inside a dedicatedextraction space to prevent any loose fibre contaminating the widerfactory area. Once impregnated the airborne loose fibres and theassociated safety and electrical hazards are eliminated.

When looking at the cost per kg to buy a pre-preg vs the dry fibre andassociated resin infusion resin, the pre-preg cost on paper is higher.It is complicated to generate the side-by-side cost as there is often acost of quality with infusion processes which generally are lessreliable than pre-preg processes. There is also significant resin wastegenerated in the injection pipe-work and other infusion consumableswhich depends on the part being manufactured.

When comparing the cost of unidirectional vs multiaxial pre-pregs, theunidirectional pre-preg has a lower cost per kg as there is no costassociated with first converting the fibre rovings into a fabric. Sowhen comparing the cost per kg of unidirectional pre-preg against aninfused uni-directional fabric the uni-directional pre-preg is costcompetitive before making a detailed analysis of the additional cost ofthe infusion processes. A larger cost per kg difference exists whencomparing a multiaxial pre-preg vs an infused multiaxial fabric makingit the cost benefit analysis less clear.

The unidirectional pre-pregs have improved mechanical propertiesallowing a fewer layers and a lighter weight beam to be used. For thisreason pre-cured uni-directional pre-preg stacks are already used inresin infused wind turbines. In current commercial manufacturingprocesses, they are first laminated into a stack, then cured, thenprepared for bonding, and then inserted at various stages into the mouldduring the lamination process. These steps add cost to the final blade.To make these pre-cured slabs handleable there is usually a maximumlength that can be processed and lifted into the mould. They are usuallycured and put in as multiple sections with longitudinally spaced scarf(i.e. tapering) joints along the blade length, which provides an area ofweakness in the blade.

There is a need in the art for a fibre-reinforced composite moulding,and method of manufacture thereof, that at least partially overcomethese problems of the manufacture of such mouldings, in particular largedimension mouldings such as wind turbine blades, which typically have alength of 30 m or more.

According to a first aspect of the present invention there is provided amethod of manufacturing a fibre-reinforced composite moulding, themethod comprising the steps of:

(a) disposing at least one layer of fibrous reinforcing material withina mould;(b) disposing at least one pre-preg layer adjacent to the fibrousreinforcing material, the pre-prep layer comprising fibrousreinforcement at least partially impregnated with uncured first resinmaterial, to form a laminar assembly of the at least one layer offibrous reinforcing material and the at least one pre-preg layer withinthe mould;(c) applying a vacuum to the assembly;(d) infusing a flowable uncured second resin material, under the vacuum,into the at least one layer of fibrous reinforcing material; and(e) curing the first and second resin materials at least partiallysimultaneously to form the fibre-reinforced composite moulding whichcomprises at least one first structural portion formed from the fibrousreinforcement and the cured first resin material bonded to at least onesecond structural portion formed from the at least one layer of fibrousreinforcing material and the cured second resin material.

Preferably, the first and second resin materials have a respectivecuring temperature range, the curing temperature ranges overlap, and thecuring step (e) is carried out at a temperature within each curingtemperature range.

The second infused resin material preferably has a curing temperaturerange that is lower than the curing temperature range of the firstpre-preg resin material. Tn one preferred embodiment, the curing step iscarried out at a temperature within the curing temperature range of thesecond infused resin material, and the curing of the second resinmaterial is exothermic and generates heat to raise the temperature ofthe first resin material to within the curing temperature range of thefirst resin material. In another preferred embodiment, the curing stepis carried out at a temperature within the curing temperature range ofthe second resin material, and the mould is heated to raise thetemperature of the first pre-preg resin material to within the curingtemperature range of the first pre-preg resin material.

Preferably, the at least one layer of fibrous reinforcing materialcomprises dry fibrous reinforcing material.

Preferably, the at least one laminar fibrous body of the at least onepre-preg layer comprises unidirectional fibres.

Preferably, in the pre-preg layer the fibrous reinforcement is fullyimpregnated with uncured first resin material.

The pre-preg layer may comprise a pre-consolidated slab of a pluralityof layers of fibrous reinforcement fully impregnated with uncured firstresin material.

Alternatively, the at least one pre-preg layer may be partiallyimpregnated and may comprise a sandwich structure of a pair of fibrousreinforcement layers on opposed sides of a layer of the uncured firstresin material.

The laminar assembly may comprise a plurality of the layers of fibrousreinforcing material interleaved with a plurality of the pre-preglayers.

Preferably, the mould has a length and a width and the layers of fibrousreinforcing material and pre-preg extend substantially continuouslyalong the length of the mould.

The method may further comprise the step, before step (a), of disposinga surfacing layer on the mould surface, the surfacing layer comprising athird uncured resin material and being in the form of at least one solidsheet, and in steps (a) and (b) the laminar assembly of the at least onelayer of fibrous reinforcing material and the at least one pre-preglayer is disposed over the surfacing layer within the mould, and in thecuring step (e) the third resin material is cured at least partiallysimultaneously with the first and second resin materials.

Preferably, the surfacing layer comprises a plurality of surfacing layersegments assembled together to form a continuous surfacing layer.

Preferably, each surfacing layer segment has at least one edge thereofthat partially overlaps an adjacent surfacing layer segment.

The third resin material of the surfacing layer may have a thickness offrom 100 to 300 microns.

The third resin material of the surfacing layer may have an appliedweight thickness of from 100 to 400 grams pre square metre (gsm).

The third resin material of the surfacing layer is supported on acarrier of a sheet material. The sheet material of the surfacing layermay have a weight of from 10 to 90 gsm,

Preferably, the sheet material of the surfacing layer comprises apolyester spun bonded scrim material.

Preferably, the sheet material of the surfacing layer is located at orproximal to a first face of the surfacing layer.

Preferably, a first face of the surfacing layer is remote from the mouldsurface so that a majority of the third resin material is between thesheet material and the mould surface.

Most preferably, the second resin material and the third resin materialhave different viscosities. The third resin material may have a higherviscosity than that of the second resin material at room temperature (20degrees Centigrade). The ratio of the viscosity, measured at 20° C.ambient temperature, of the third resin material and of the second resinmaterial may be at least 100/1, more preferably at least 1000/1, yetmore preferably at least 10,000/1.

Preferably, in the curing step (e) the second resin material is adaptedto initiate curing before the third resin material.

The curing step (e) may be carried out at an elevated temperature aboveroom temperature, preferably at a temperature of from 40 to 90 degreesCentigrade.

Preferably, in the curing step (e) the curing reaction of the secondresin material is exothermic which generates heat which accelerates thecuring of the third resin material.

The third resin material may be a thermosetting epoxy resin, and/or thefirst resin material and the second resin material may be thermosettingepoxy resins.

The fibre-reinforced composite moulding may particularly be a windturbine blade.

According to a second aspect of the present invention there is provideda fibre-reinforced composite moulding comprising a structural laminatedportion being formed from at least one first layer, the first layerbeing formed from a pre-preg and comprising fibrous reinforcement andcured first resin material, laminated with at least one second layer,the second layer comprising fibrous reinforcing material and a curedsecond resin material, wherein the first and second resin materials aremutually bonded by having been cured at least partially simultaneously.

Preferably, the fibrous reinforcement comprises unidirectional fibres.

The structural laminated portion may comprise a plurality of the firstlayers interleaved with a plurality of the second layers.

Preferably, the moulding has a length and a width and the fibrousreinforcement and the fibrous reinforcing material extend substantiallycontinuously along the length of the moulding.

The fibre-reinforced composite moulding preferably further comprises asurface portion laminated to the structural portion, the surface portionbeing formed of a surfacing layer comprising a plurality of surfacinglayer segments moulded together to form a continuous surfacing layer,the surfacing layer comprising a third cured resin material supported ona carrier of a sheet material,

The sheet material of the surfacing layer may be located nearer to aninterface between the surface portion and the structural portion than toan opposite exposed surface of the surface portion.

The fibre-reinforced composite moulding is most preferably a windturbine blade.

The present invention is predicated on the finding by the inventor thatby using, in particular embodiments, the combination of an ambienttemperature curing infusion resin and a higher temperature curingpre-preg resin in a laminate structure, the pre-preg resin can bereadily cured, even in relative thick sections of the mould, byreceiving additional heat either from the exothermic curing of theinfusion resin and/or from heating the tool. The result is that uncuredpre-pregs can be combined with a VARTM infusion process in a veryefficient improved manufacturing process in which the two resins,infusion and pre-preg, can be cured together in a common curing step. Nopre-curing of the pre-preg is required.

This also provides an improved product, for example for long and/orthick mouldings such as wind turbine blades or bridge decks. For longmouldings, the pre-pregs can be incorporated as very long lengths,because they include uncured resin, and so have not had to be sectionedinto smaller units for a precuring step, and also are mechanicallyflexible and so can be accommodated as long lengths with some degree ofcurvature within the mould. Accordingly, continuous lengths of pre-pregcan be applied directly into the mould during the lay-up stage to avoidthe scarf joint problem. The final cure step for the pre-preg resin thenoccurs with the cure of the infused resin of the remainder of thecomposite laminate.

This contrasts with the known use of smaller cured pre-preg lengths. Thelonger pre-preg lengths give improved mechanical properties becausemultiple scarf joints, as discussed above with known pre-pregincorporation, can be avoided. For some products, even very long (30metres plus, up to about 50 metres) wind turbine blades, the pre-pregcan extend as a single length along the entire moulding length withoutany longitudinally spaced joints.

It is alternatively possible for the method of the invention to provide,for some products, a plurality of individual pre-preg segmentsinterconnected along the length of the mould using the taperinginterlocking ends of the known scarf structure and this would stillprovide manufacturing advantages over the known method of usingpre-preps as discussed above. In such a method of the these embodimentsof the present invention, the pre-pregs are pre-consolidated in a fasterprocess as compared to the known pre-curing process, rather than cured,to both remove air between the layers and give a handleable stack toplace into the mould. Again, the final cure step for the pre-preg resinthen occurs with the cure of the infused resin of the remainder of thecomposite laminate.

In accordance with preferred embodiments of the present invention, anelevated curing temperature uncured thermoset epoxy resin surfacingfilm, having relatively high viscosity, can be first laminated into amould, dry fibre is then applied together with the pre-preg layer(s)including uncured pre-preg resin, preferably also thermoset epoxy resin,and then the dry fibre is impregnated with a relatively low viscosityambient temperature curing resin, preferably also thermoset epoxy resin,by a VARTM infusion process. The mould temperature and/or the ambientair temperature may be raised so the three resin materials can co-curetogether.

In one arrangement, the temperature of the mould and/or the surroundingair are increased such that the temperature activation point of theelevated curing thermoset epoxy resin surface film, if present, and thepre-preg resin is reached and the resin materials can co-cure.

In another arrangement, the ambient temperature curing resin which hasbeen infused generates sufficient exothermic heat so that thetemperature of the stack increases and the temperature activation pointof the elevated curing thermoset epoxy resin surface film, if present,and the pre-preg resin is reached and the resin materials can co-cure.

In further arrangement, a combination of increasing the temperature ofthe mould and/or the surrounding air is employed, thereby increasing therate of reaction of the ambient temperature curing infused resin, sothat the exothermic heat is produced at a faster rate causing a greaterrise in the laminate temperature which can exceed the resin inputtemperature. This then causes the activation temperature of the elevatedcuring temperature thermoset epoxy of the pre-preg to be exceeded andthe materials can co-cure and a faster rate.

This underlying technical concept of the present invention thereforecombines an elevated temperature curing pre-preg with dry fibrous layerswhich are then infused with low temperature curing resin and the tworesins are co-cured. As the pre-preg stack, preferably UD, isinterleaved with dry fibre which infuses with the ambient curing resin,this enhances the warm-up of the pre-preg stack due to the exothermicheat generation from the curing infused resin. This in turn helps toincrease the pre-preg stack temperature more quickly to achieve therequired minimum curing temperature, thereby speeding up the cycle time.

What generally prevents some current elevated curing temperaturepre-pregs, for example curing at 70 to 90 degrees Centigrade, from beingused commercially on a low temperature tool, adapted to be used at lowertemperatures, typically about 20 to 40 degrees Centigrade, is that thelow temperature required so as not to damage the tool results in a slowcure rate of the pre-preg at the tool temperature. There is also aconcern to avoid any high exothermic heat resulting from curing of theresin of the pre-preg in the thickest section overheating the tool.

However, in the thick sections of the laminate, the high exothenntemperature reached tends to be isolated from the tool surface, sincethe peak temperature occurs in the laminate centre. Therefore a level ofexothenn temperature above the tool Tg can be tolerated.

A fast cycle time can be designed by tuning the activation and cure rateof the pre-preg to match the thinner section (typically 3-5 mm thick)where the surface temperature of the laminate is nearly equal to thepeak temperature of the laminate at its centre. In such a case, thelimiting process time is the cure rate of the pre-preg at the maximumtool temperature.

In some tools for producing turbine blades for us in wind energygenerators, a water heating pipework is provided within the tool forlimiting the final mould temperature. In particular the rate oftemperature increase of the tool slows dramatically as the toolapproaches the temperature of the water input, because there is nolonger a significant temperature difference driving the heat transfer tothe tool surface from the exothermically heated moulding as the resincures. The exothermic heat generation of the infusion laminate is highlybeneficial in these tools, because a laminate temperature in excess ofthe water input temperature can be reached to activate and cure thepre-preg resin. The pre-preg resin can then begin its own exothermicreaction and the laminate temperature in excess of the heat input can bemaintained for a faster cure within the tool Tg limit.

This expedient would work with pre-pregs having a curing temperature forexample of greater than about 90 degrees Centigrade, but the resincuring rate would be rather slow. For methods employing low temperaturetools and typically a 60-70 degrees Centigrade pre-preg system, thecuring rate would be satisfactory. The higher cost, lower temperature,curing agent employed in the pre-preg resin to make it cure at lowertemperature may be employed commercially in combination with the UDpre-preg. This is because the relatively higher cost resin is offset bythe UD pre-preg which can use lower cost rovings, because there is nofabric conversion cost. In contrast, fabric pre-pregs have a higherpre-preg cost, and so combining these with a more expensive curing agentis less commercially viable.

Preferred embodiments of the present invention provide interleaving dryfibre and UD pre-preg layers within a mould, fitting core materials tothe interleaved layers, and then using a resin infusion process toimpregnate the dry materials and bond the core materials to form aunitary composite material.

Preferred embodiments of the present invention also provide that byraising the temperature to co-cure one or more uni-directional pre-pregsincorporating relatively high temperature curing resin and relativelylow temperature curing, in particular ambient temperature curing,infusion resin by heating the tool (and also the vacuum bag face ifrequired) so that that the activation temperature of the pre-preg resinis reached and the exothermic heat generation of the infusion resin andthe pre-preg resin can assist a more rapid cure of the pre-preg resin.

Preferred embodiments of the present invention have particularapplication in the production of wind turbine blades, or beams requiringthick UD sections, such as bridge decks.

Preferred embodiments of the present invention can also provide theadvantage that low cost, well aligned unidirectional fibres can beapplied into a mould to improve the mechanical properties of a beam likestructure, for example a wind turbine blade, while still using low costresin infusion process for the remaining laminate. Tn addition, thepreferred embodiments of the present invention provide can provide theadvantage of removing the problems associated with the use of a UDpre-preg with a resin curing activation temperature close to the maximumheat rating or heat input of the tool.

Preferred embodiments of the present invention can further provide theadvantage that improved properties of the pre-preg component of thecomposite laminate can be achieved without requiring a pre-curing stepfor the pre-preg and also allowing the possible use, where the mouldedarticle requires this, of a continuous pre-preg along the full length ofthe article, for example a wind turbine blade, which may typically be upto 50 m long.

Preferred embodiments of the present invention can further provide theadvantage that can increase the cure rate of the pre-preg resin, lowerthe overall cure temperature within the mould and therefore enable theuse of a lower temperature, and consequently a lower cost, mouldingtool.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying Figures, in which:

FIG. 1 is a cross-sectional view, in the width direction of the mould,of an arrangement of a plurality of overlapping surfacing films formedin a first step of an embodiment of the method of the present invention;

FIG. 2 is a cross-sectional view, in the length direction of the mould,of the surfacing films of FIG. 1;

FIG. 3 is a cross-sectional view, in the width direction of the mould,of the surfacing films of FIG. 1 subsequently covered by a first twolayers of dry fabric reinforcements in a second step of the embodimentof the method of the present invention;

FIG. 4 is a cross-sectional view, in the length direction of the mould,of the assembly of FIG. 3;

FIG. 5 is a cross-sectional view, in the width direction of the mould,of the assembly of FIG. 3 subsequently covered by a pre-preg layer andadditional dry fabric reinforcements in a subsequent step of theembodiment of the method of the present invention;

FIG. 6 is a cross-sectional view, in the length direction of the mould,of the assembly of FIG. 5; and

FIG. 7 is an exploded plan view, partly in phantom, of an arrangement ofa plurality of overlapping surfacing films and layers of overlapping dryfabric reinforcements formed, the overlapping in each case being in thelength direction of the mould and in the width direction of the mould,in accordance with a further embodiment of the method of the presentinvention.

In accordance with the preferred embodiments of the present invention,the basic manufacturing process for the fibre-reinforced compositemoulding includes the steps of: preparing a mould and applying a releaseagent;

optionally placing in the mould a surfacing layer comprising a surfacingresin film in the form of at least one solid sheet, with preferableoverlaps between adjacent segments of the surfacing layer, the surfacinglayer optionally being provided in combination with a dry fabricreinforcement layer adjacent to the surfacing layer which is pre-tackedto the surfacing layer;placing in the mould, over the surfacing layer, a structural layercomprising structural dry fabric reinforcements, with preferableoverlaps between adjacent segments of the structural layer;placing in the mould, over the structural layer, at least one partiallyor fully impregnated pre-preg layer comprising fibre reinforcements andresin material, most preferably unidirectional fibre reinforcementsextending along the length direction of the mould;optionally placing over the structural layer additional structural dryfabric reinforcements and/or pre-preg layers to form an interleavedstructure of these layers,optionally placing a core material over the structural and pre-preglayers;placing and connecting a resin feed infusion system;covering the mould with a peel ply, a release film, an optional infusionmesh and a vacuum bag;debulking the system under full vacuum;conditioning the system at the resin infusion temperature to removeremaining entrapped air and to soften the surfacing resin film;creating a pressure differential across the system and using thepressure differential to feed a resinous compound into the system tocoat the fibrous reinforcement capable of being infused;ceasing the feeding of the resinous compound into the system;maintaining some pressure differential; andallowing the resinous compound, the pre-preg resin and the surfacingresin film when present to set and cure.

A more detailed explanation of the process steps in accordance with oneparticular embodiment is described with reference to FIGS. 1 to 6 of thedrawings. In this illustrated embodiment, surfacing layers are initiallyapplied into the mould and the surfacing resin is co-cured with theinfusion resin. However, the surfacing layers may be omitted, andinstead a conventional gel coat may be used to provide the surface ofthe moulding.

FIGS. 1 and 2 show the preferred layout for the surfacing layersdepending on their location in a mould. Referring to FIGS. 1 and 2,after preparing a mould and applying a release agent (not shown) to themould surface 10, a surfacing layer 12 is applied to the mould surface10. The surfacing layer 12 comprises a surfacing resin layer 14 in theform of at least one solid sheet that is carried on a layer 16 of scrimmaterial to assist resin retention of the mould surface 10. Typicallythe scrim layer 16 is a polyester material, such as a polyester veil 16.

In the illustrated embodiment, the surfacing layer 12 comprises aplurality of surfacing layer segments 106, 206, 306 assembled togetherto form a continuous surfacing layer 12 in the form of plural solidsheets.

When assembling the surfacing layer 12 onto the mould surface 10, afirst segment 106 is overlapped by a second segment 206 in the widthdirection of the mould, the overlap forming a lower covered edge portion107 of the first segment 106 and an upper covering edge portion 207 ofthe second segment 206. In turn, the second segment 206 is overlapped bya third segment 306 in the width direction of the mould, the overlapforming a lower covered edge portion 208 of the second segment 206 andan upper covering edge portion 307 of the third segment 306.Accordingly, the opposing edge portions 207, 208, longitudinallydirected along the mould, of the second segment 206 have an overlapping,over or under respectively, relationship with an edge portion 107, 307of the respective adjacent segment 106, 306.

Although not illustrated, if there are further segments in the widthdirection, this overlapping configuration is repeated across the widthof the mould for successive segments.

In the length direction of the mould, it is possible to have differentconfigurations of the surfacing layer. In many embodiments, a continuouslength of surfacing layer can be disposed along the length of the mould,and where possible this may be preferable to reduce lay-up time, forexample. In other alternative embodiments, the surfacing layers canoverlap or abut in the length direction of the mould.

However in this particular embodiment, in the length direction of themould, there is an abutting relationship. Referring back to thedrawings, adjacent to the first segment 106 is a fourth segment 406. Thefourth segment 406 abuts and is positioned flush with the edge of thefirst segment 106. Correspondingly, a fifth segment 506 abuts the fourthsegment 406 and is positioned flush with the edge of the fourth segment406.

Each surfacing layer segment 106, 206, 306, 406, 506 comprises asurfacing resin layer segment 105, 205, 305, 405, 505 that is carried ona scrim material segment 104, 204, 304, 404, 504.

Again, although not illustrated, if there are further segments in thelength direction, this abutting configuration is repeated across thelength of the mould for successive segments.

Additional segments are disposed in the mould, in an overlappingrelationship in one direction, and in an abutting relationship inanother direction, so as to cover the entire mould surface. The pluralsurfacing layer segments 106, 206, 306, 406, etc. therefore form asegmented continuous surfacing layer 12 in the form of a plurality ofsolid sheets.

In an alternative embodiment, there may be such an overlappingrelationship for the surfacing films in two mutually orienteddirections, for example in the length direction of the mould as well asthe width direction of the mould which is orthogonal thereto. This canprovide that all of the surfacing layer edges have an overlappingrelationship, except at the extremities of the mould.

Referring to FIGS. 3 and 4, after the surfacing layer 12 has beenformed, a structural layer 22 comprising at least one layer 24, 26 ofdry fibrous reinforcing material is disposed on the surfacing layer 12to provide, on the portion of the mould surface 10, an assembly, in theform of a laminar stack, of the surfacing layer 12 and structural layer22. The dry fibrous reinforcing material may be selected from one ormore of glass fibre, aramid fibre, carbon fibre, flax, or jute, ormixtures thereof.

The at least one layer 24, 26 of fibrous reinforcing material may besegmented and subsequently positioned above the surfacing layer 12 in anoverlapping segmented configuration, similar to that for the surfacinglayer 12, to provide a venting structure and allow entrapped air to passout during subsequent resin infusion processing.

In the overlapping segmented configuration, a respective segment stackof dry reinforcement layers 102, 103; 202, 203; 302, 303 is located overthe respective surfacing layer segment 106; 206; 306.

Initially, a segment stack of dry reinforcement layers 102, 103 isdisposed over the first surfacing layer segment 106.

The lowermost dry reinforcement layer 103 of the first stack segment isshaped and dimensioned so as to cover that portion of the upper surfaceof the first surfacing layer segment 106 which is exposed, and so abutsthe edge portion 207 of the second segment 206. The next dryreinforcement layer 102 is placed over the first dry reinforcement layer103 and is shaped and dimensioned so as to cover the lowermost dryreinforcement layer 103 and, by an edge portion 108 of the next dryreinforcement layer 102, the edge portion 207 of the second segment 206.

Subsequently, a second segment stack of dry reinforcement layers 202,203 is disposed over the second surfacing layer segment 206.

The lowermost dry reinforcement layer 203 of the second stack segment isshaped and dimensioned so as to cover that portion of the upper surfaceof the second surfacing layer segment 206 which is exposed, and so abutsthe edge portion 307 of the third segment 306, and also so as to coverthe edge portion 108 of the dry reinforcement layer 102. The next dryreinforcement layer 202 is placed over the lowermost dry reinforcementlayer 203 and is shaped and dimensioned so as to cover the loweiinostdry reinforcement layer 203 and, by an edge portion 208 of the next dryreinforcement layer 202, the edge portion 307 of the third segment 306.

Subsequently, a third segment stack of dry reinforcement layers 302, 303is disposed over the third surfacing layer segment 306.

The lowermost dry reinforcement layer 303 of the third stack segment isshaped and dimensioned so as to cover that portion of the upper surfaceof the third surfacing layer segment 306 which is exposed, and so as tocover the edge portion 208 of the dry reinforcement layer 202. The nextdry reinforcement layer 302 is placed over the lowermost chyreinforcement layer 303 and is shaped and dimensioned so as to cover thelowermost dry reinforcement layer 303.

If there are further segments across the width of the mould, subsequentsegment stacks of dry reinforcement layers are correspondingly appliedin an overlapping configuration.

In the length direction of the mould, as for the surfacing layer it ispossible to have different configurations of the dry reinforcementlayers. In many embodiments, a continuous length of dry reinforcementlayer can be disposed along the length of the mould over the surfacinglayer, and where possible this may be preferable to reduce lay-up time,for example. This continuous dry reinforcement can provide improvedmechanical properties in the length direction, particularly for a windturbine blade, because of the absence of longitudinally spaced joints inthe dry reinforcement. In other alternative embodiments, the dryreinforcement layers can overlap or abut in the length direction of themould.

However in this particular embodiment, in the length direction of themould, there is an abutting relationship. Referring back to thedrawings, the fourth segment 406 is correspondingly covered by dryreinforcement layers 402, 403 that abut and are positioned flush withthe edges of the dry reinforcement layers 102, 103. Correspondingly, thefifth segment 506 is covered by dry reinforcement layers 502, 503 thatabut and are positioned flush with the edges of the dry reinforcementlayers 402, 403 over the fourth segment 406.

Again, although not illustrated, if there are further segments in thelength direction, this abutting configuration of the dry reinforcementlayers is repeated across the length of the mould for successivesegments.

The structural dry reinforcement layers are disposed in the mould overthe respective surfacing segments, in an overlapping relationship in onedirection, and in an abutting relationship in another direction, so asto cover the entire mould surface. This forms a segmented continuousstructural layer 22.

In an alternative embodiment, there may be such an overlappingrelationship for the structural dry reinforcement layers in two mutuallyoriented directions, for example in the length direction of the mould aswell as the width direction of the mould which is orthogonal thereto.This can provide that all of the structural dry reinforcement layeredges have an overlapping relationship, except at the extremities of themould. The selection of the particular overlapping relationship candepend on the structure and composition of the dry fabric reinforcementlayers, and the particular nature and end application of the articlebeing manufactured.

The provision of such an overlapping relationship for the structural dryreinforcement layers in two mutually oriented directions may be providedwith either of the two overlapping configurations for the surfacinglayer disclosed above, i.e. with the surfacing layer overlapping in onlyone direction or in two mutually oriented directions.

FIG. 7 is an exploded plan view, partly in phantom, of an arrangement ofa plurality of overlapping surfacing films and layers of overlapping dryfabric reinforcements formed, the overlapping in each case being in thelength direction of the mould (x) and in the width direction of themould (y), in accordance with a further embodiment of the method of thepresent invention. The surfacing film 700 includes a plurality ofsegments 702 that overlap on adjacent edges 704, 706, oriented in twoorthogonal directions (x and y).

Each of three stacked layers 708, 710, 712 of dry fabric reinforcementincludes a respective plurality of segments 714, 716, 718 that alsooverlap on adjacent edges 720, 722; 724, 726; 728, 730, oriented in twoorthogonal directions. As discussed herein, in such a stack ofoverlapped segments the dry fabric reinforcement layers are typicallybiaxial and/or triaxial dry fabric reinforcement layers.

It will be apparent to the skilled person that the illustratedembodiment incorporates two structural dry reinforcement layers butfewer or more layers, and core materials such as wood and foam, may beemployed if desired.

In an alternative embodiment, a first layer of reinforcement fibre maybe initially adhered, by tacking, to the surfacing layer segments thatare laid down onto the mould surface. Accordingly the first layersdisposed in the mould are integral resin surfacing and fibrereinforcement layers. This embodiment can reduce the total lay-up timerequired to assemble all of the layers to form the laminate in themould.

Referring to FIGS. 5 and 6, at least one pre-preg layer 101 is thendisposed over the structural layer 22. The pre-preg layer 101 is notshown to scale, for the purpose of clarity of illustration. The pre-preglayer 101 comprises fibre reinforcements 800, most preferablyunidirectional fibre reinforcements extending along the length directionof the mould, adhered to an uncured pre-preg resin 801. The pre-preglayer 101 preferably comprises a sandwich structure of two opposedlaminae of outer fibre reinforcements 800 with a central uncuredpre-preg resin layer 801 therebetween. In the pre-preg layer 101 thefibre reinforcements 800 may be partly or fully impregnated by theuncured resin 801. Plural pre-preg layers 101 may be stacked together.One or more additional structural dry reinforcement layers 100 aredisposed over the pre-preg layer(s) 101. This forms an interleavedstructure between the structural dry fabric reinforcements and/or UDpre-preg layers to form an interleaved structure of these layers.

At least one additional layer, for example a foam core (not shown)and/or one or more additional structural dry reinforcement layers (notshown) may be placed over the interleaved structure. This completes thelaminate stack 30 which is now ready for resin infusion, as shown inFIG. 6.

The embodiment illustrated in FIGS. 1 to 6 preferably incorporates atriaxial dry fabric reinforcement structure, in which the fibres of thestructural dry reinforcement layers are oriented in three respectiveaxial directions. However in alternative embodiments, the configurationof the dry fabrics structural reinforcement layers may be different. Forexample, the structural dry fabrics could either be unidirectional (UD),biaxial or triaxial in orientation. The overlaps of the dry fabricswould generally exist in the both the width and length directions forbiaxial and triaxial orientations. In general, unidirectional (UD)fabrics overlap in the width direction, whereas in the length directionsuch overlap is not necessary and would generally only occur if, duringlay-up of the fabric into the mould, there is a short fabric roll andthe fabric stops in the middle of the mould.

The resin infusion is then carried out in a manner known to thoseskilled in the art. In particular, the assembly of surface, structural,pre-preg and additional layers on the mould is covered with, in turn, apeel ply, a release film and an optional infusion mesh to increase theimpregnation speed in selected parts of the laminate. Then the entiremould assembly is disposed within a vacuum bag. A resin feed infusionsystem is connected to the bag, the bag having an upstream portconnected to a source of resinous compound and a downstream portconnected to a source of vacuum. The vacuum is applied to the vacuum bagwith the upstream port closed thereby to debulk the system under fullvacuum. If necessary, any leaks are identified and repaired if present.The vacuum is maintained at a desired level in order to condition thesystem at the resin infusion temperature to remove remaining entrappedair and soften the surfacing resin film. Then the upstream port isopened, thereby creating a pressure differential across the system. Thepressure differential acts to feed a liquid resinous compound from thesource of resinous compound into the system to coat the fibrousreinforcement. In this way, the resinous compound is infused completelyinto the dry fibrous reinforcement layers. Sufficient structuralinfusion resin is fed to the system to fully impregnate the fibres.Finally, the feeding of the resinous compound into the system isterminated, and full vacuum is applied to the system.

The infused structural resin then increases in viscosity and begins tocure after a time period governed by the resin reactivity and the amountof heat applied to the laminate. Alternatively the vacuum may be reducedif the resin has a long gel time to prevent the resin being drained outof the laminate. Additional heat can be applied during, or after, resininjection to speed up the curing process of the structural resin andactivate the cure of the surface and pre-preg resins.

The pre-preg and infused structural resin materials are cured at leastpartially simultaneously. The structural portion formed from thepre-preg is bonded to the structural portion formed from dry fibrousreinforcing material by the co-cured pre-preg resin material andinfusion resin material. The pre-preg and infused structural resinmaterials have a respective curing temperature range, and the curingtemperature ranges overlap, and the curing step is carried out at atemperature within each curing temperature range. The infused resinmaterial has a curing temperature range that is lower than the curingtemperature range of the pre-preg resin material. The curing step may becarried out at a temperature, e.g. at an ambient temperature of forexample 20 degrees Centigrade, or at an elevated temperature, forexample up to 40 degrees Centigrade, within the curing temperature rangeof the infused resin material. The curing of the infused resin materialis exothermic and generates heat to raise the temperature of thepre-preg resin material to within the curing temperature range of thepre-preg resin material. Optionally, the mould is additionally heated toraise the temperature of the pre-preg resin material to within thecuring temperature range of the pre-preg resin material. This canfurther accelerate the cure of the pre-preg resin.

When a surfacing layer of uncured resin is initially disposed on themould surface, the surfacing layer uncured is, in the curing step, curedat least partially simultaneously with the pre-preg and infused resinmaterials. Again, exothermic heat from the curing infused resin caninitiate or accelerate the cure of the surface resin, and optionally themould may be heated to accelerate the curing further.

After complete curing of the structural infusion resin, the pre-pregresin and, when present, the surface resin, the vacuum is removed, thevacuum bag is opened, the peel ply, release film and infusion mesh areremoved, and the laminate is released from the mould. When the surfaceresin is present, the surface of the laminate, substantially ready forpainting, comprises the cured surface resin and the scrim layer.Alternatively, a gelcoat may be present as known in the art.

The surfacing resin 14 is selected such that it is air permeable toprovide an additional pathway for the removal of air during theevacuation process. The thickness of the surfacing layer 12 ispreferably selected to be 100-400 microns, more preferably 100-300microns. Within this thickness range it has been found that thesurfacing resin 14 can be made partially air permeable. If the surfacingresin layer 14 is too thin then a sufficient thickness barrier is notobtained between the fibre reinforcement and the subsequently appliedpaint causing a pattern of the underlying fibres, known as a printpattern, potentially to appear on the resin surface. If the layer is toothin, this can lead to dry fibre close to the surface that can causeproblems when sanding the surface prior to painting. The resulting dryglass fibre particles can get trapped on the abrading tool (e.g. a disc)and are very abrasive, which can lead to scratch marks, in turnrequiring repeated abrasive tool changes and additional filling andfairing repair steps prior to painting.

The air between the mould surface 10 and the surfacing layer 12 can passthrough the surfacing layer 12 and into the more highly air permeabledry fibre layers 102 and 103, to then be drawn away into the vacuumsource. It is not essential that an air breathing scrim 16 is providedin the surface layer 12 so as to be located substantially at the mouldsurface 10. However, the use of a scrim 16 provides the advantage thatthe tack of the surface resin 14 is more consistent and depends only onthe resin formulation of the surface resin 14 which is formulated togive the desired and consistent tack level. The fine polyester scrim 16within the surfacing layer 12 serves two purposes. First, it helpsprevent fibres of the structural fibre reinforcement from entering thesurface resin layer 14. Moreover, the fine weave layer helps prevent theresin 14 in the surfacing layer 12 reticulating off the mould surface 10giving a better quality of finish to the surface of the resultantlaminate. The polyester scrim. 16 is itself easy to sand and does notresult in abrasive particles damaging the surface.

The dry reinforcement layers provide one or more highly permeable airventing paths to remove air when a vacuum is applied to the laminatestack. As the pieces of material are overlapped the surface layer is nowin connection with the highly air permeable dry fibre layer allowing amore direct and effective air path to the vacuum source. The overlappingzone allows more effective connection of the dry reinforcement to give ahighly permeable venting structure. The continuous surface resinprevents defects occurring at the point of overlap of the material. Thezone is an important feature of the present invention, and is necessaryfor heavier weight fabrics above 600 gsm. Without the overlapping zonethe air permeability across the overlapped fabric is reduced leading todefects in larger components.

As well as providing a thickness buffer to avoid fibre print, thesurface resin layer 14 provides a protective barrier for reducingmoisture ingress into the laminate. Fibre strands, in particular ofglass fibre, close to the surface can accelerate moisture ingress by awicking mechanism.

The surface resin 14 may be toughened and the modulus reduced by theincorporation of rubber, for example, into the resin. This is aparticular advantage as this helps to prevent cracks from any mismatchin thermal expansion between the subsequently-applied paint and thelaminate. The tailored surface resin helps improve paint chipping thatoccurs in impact situations.

The overlapping configuration of the dry reinforcement layers 102, 103,202, 203, 302, 303 provides one or more highly permeable air ventingpaths to remove air when a vacuum is applied to the laminate stack. Asthe pieces of material are overlapped, the edge portion 207 of thesurfacing layer 206 is directly in connection with the highly airpermeable dry fibre layer 102 allowing a more direct and effective airpath to the vacuum source in subsequent processing, as discussed below.

The overlapping zone allows more effective connection between the dryreinforcement layers 102, 103, 202, 203, 302, 303 to give a highlypermeable venting structure. The continuous surfacing segment layers106, 206, 306 including the surfacing resin layer segments 105, 205, 305prevent defects occurring at the point of overlap of the material.

Due to the venting structure the trapped air is removed by theapplication of vacuum to the material and the cured surface layer isvirtually free of voids. This resultant surface structure has been foundto reduce the rate of coating erosion.

The structural infusion resin and surface resin have a differentviscosity. The viscosity of the structural infusion resin is usuallyselected to be lower than that of the surface resin at infusiontemperature, so that the structural infusion resin can readily beinfused without the vacuum disrupting the surface resin layer. Theviscosity of the surface resin is higher than the structural infusionresin to ensure that the surface resin stays closer to the mould surfaceto maintain the thickness of the surface layer in the final component.

Materials with different viscosity profiles can be made to work byadjusting the cure cycle provided a differential viscosity existsbetween the surfacing resin layer and structural infusion resin.

The surfacing film is required to have a relatively high minimumviscosity to prevent premature wet-out of the dry fibre reinforcementprior to termination of the resin infusion step. The viscosity must alsobe sufficiently high to stop the dry fibre reinforcement moving to thesurface. The viscosity must also be sufficiently high to ensure that thesurfacing layer remains as a coherent resin layer during the compositemoulding material production process. However, the viscosity must not betoo high otherwise the wettability of the mould surface by the surfacingresin may be inadequate. The surfacing resin should also have asufficient degree of flow to enable the solid resin layer to fill anyminor discontinuities or voids at any overlaps between the separatesurfacing sheet segments when the surfacing layers are subjected tovacuum processing prior to curing. The surfacing resin should also havea good cold-flow resistance to enable the solid resin layer in sheetform to be stored on a roll, and have a good shelf-life and productstability. The surfacing resin should also have a good abrasionresistance (typically measured in a Taber abrasion test) to permit somedegree of surface abrasion, for example sanding of the primer surfaceresin layer prior to painting, whilst maintaining surface toughness andintegrity.

Typically, the surfacing resin has a viscosity of from 0.1×10⁵ to 5×10⁵Pa·s measured at 20° C.

The structural infusion resin in contrast has a lower viscosity toenable it readily to be infused under vacuum into the dry fibrousreinforcement layers.

Typically, the structural infusion resin has a viscosity of from 0.1 to2 Pa·s measured at 20° C., preferably from 0.1 to 0.6 Pa·s.

In this specification, the resin viscosity of the structural infusionresin is measured using a TA Instruments AR2000 rheometer with a 40 mmdiameter aluminium 2° cone and a Peltier cooling system. The experimentwas carried out under the following conditions: a course shear ratesweep experiment at 20° C. from 0.01 s⁻¹ to 500 s⁻¹ with a gap of 57 μm.The viscosity of the material was taken as an average during the linearNewtonian region between 1-100 s⁻¹.

In this specification the resin viscosity of the surfacing resin ismeasured using a TA Instruments AR2000 rheometer with a 20 mm diametersteel plate and a Peltier cooling system. The experiment was carried outunder the following conditions: oscillation experiment from 40° C. downto 0° C. at 2° C./min with a controlled displacement of 1×10⁻⁴ rads at afrequency of 1 Hz and a gap of 1000 μm.

Moreover, the structural infusion resin has a viscosity to enable itreadily to be infused under vacuum conditions that in contrast do notcause any significant spreading or flow of the surfacing resin. Thesurfacing resin should have a viscosity that is higher than thestructural infusion resin so that the surfacing resin cannot wet thestructural reinforcement before the surfacing resin (i.e. the surfacingresin must be thick enough to achieve this technical effect), but theviscosity should be low enough so that the surfacing resin can exhibit aminor degree of spreading and flow on the mould surface and thereby canassist with air removal under the vacuum processing (i.e. the surfacingresin must be thin enough to achieve this technical effect).

Preferably, the ratio of the viscosity, measured at 20° C. ambienttemperature, of the surfacing resin and of the structural infusion resinis at least 100/1, more preferably at least 1000/1, yet more preferablyat least 10,000/1.

The structural infusion resin has a slow reactivity at the infusiontemperature to allow full impregnation of the dry fibrous reinforcementlayers. The pre-preg resin, and when present the surface resin, begin tocure after the infusion resin initiates curing. This is achieved byexothermic heat generation from the curing infusion resin heating thepre-preg and surface resins to activate the curing mechanism and/or byheating the tool on which the surface resin is disposed. The pre-preg,surface and structural infusion resins continue to cure together atleast partially simultaneously which promotes a high level of adhesionbetween the different resin materials.

The surface resin is preferably selected from the group consisting ofthermoset resins such as epoxy, cyanate ester and phenolic resins.Suitable epoxy resins include diglycidyl ethers of bisphenol A,diglycidyl ethers of bisphenol F, epoxy novolac resins and N-glycidylethers, glycidyl esters, aliphatic and cycloaliphatic glycidyl ethers,glycidyl ethers of aminophenols, glycidyl ethers of any substitutedphenols and blends thereof. Also included are modified blends of theaforementioned thermosetting polymers. These polymers are typicallymodified by rubber or thermoplastic addition. Any suitable catalyst maybe used. The catalyst will be selected to correspond to the resin used.One suitable catalyst for use with an epoxy resin is a dicyandiamidecuring agent. The catalyst may be accelerated. Where a dicyandiamidecatalyst is used, a substituted urea may be used as an accelerator.Suitable accelerators include Diuron, Monuron, Fenuron, Chlortoluron,bis-urea of toluenedlisocyanate and other substituted homologues. Theepoxy curing agent may be selected from Dapsone (DDS), Diamino-diphenylmethane (DDM), BF3-amine complex, substituted imidazoles, acceleratedanhydrides, metaphenylene diamine, diaminodiphenylether, aromaticpolyetheramines, aliphatic amine adducts, aliphatic amine salts,aromatic amine adducts and aromatic amine salts.

The surface material can be provided with a toughening agent. Suitabletoughening agents can be selected from liquid rubber (such as acrylaterubbers, or carboxyl-terminated acrylonitrile rubber), solid rubber(such as solid nitrite rubber, or core-shell rubbers), thermoplastics(such as poly (EtherSulphone), poly (Imide)), block copolymers (such asstyrene-butadiene-methacrylate triblocks), or blends thereof.

The structural infusion resin is preferably selected from the groupconsisting of thermoset resins such as epoxy, cyanate ester and phenolicsystems. Suitable epoxy resins include diglycidyl ethers of bisphenol A,diglycidyl ether of bisphenol F, glycidyl ethers of any substitutedphenols, higher molecular weight of any of those molecules, epoxynovolac resins and glycidyl esters, aliphatic and cycloaliphaticglycidyl ethers, glycidyl of aminophenols, glycidyl amine and blendsthereof.

Reactive or non reactive diluents can also be used. Reactive diluentsmay include monofunctional or multifunctional reactive diluents such asC12-C14 glycidyl ether or butane diol diglycidyl ether. Non reactivediluents may include nonyl phenol, furfuryl alcohol, dibutyl phthalatem,polymethyl acetal.

Also included are modified blends of the aforementioned thermosettingpolymers, with such modifiers as liquid rubber (such as acrylaterubbers, or carboxyl-terminated acrylonitrile rubber), solid rubber(such as solid nitrite rubber, or core-shell rubbers), thermoplastics(such as poly (EtherSulphone), poly (Imide)), block copolymers (such asstyrene-butadiene-methacrylate triblocks), or blends thereof.

The curing agent or catalyst will be selected to correspond to the resinused. Suitable curing agents are aliphatic amines, cycloaliphaticamines, aromatic amines, polyamides, amidoamines, polysulfides,anhydride and any suitable adduct of Suitable catalyst may includesalicylic acid, aliphatic tertiary amines, and aminoethylpiperazine.

One suitable latent catalyst for use with an epoxy resin is adicyandiamide curing agent. The catalyst may be accelerated. Where adicyandiamide catalyst is used, a substituted urea may be used as anaccelerator. Suitable accelerators include Diuron, Monuron, Fenuron,Chlortoluron, bis-urea of toluenedlisocyanate and other substitutedhomologues. The epoxy curing agent may be selected from Dapsone (DDS),Diamino-diphenyl methane (DDM), BF3-amine complex, substitutedimidazoles, accelerated anhydrides, metaphenylene diamine,diaminodiphenylether, aromatic polyetheramines, aliphatic amine adducts,aliphatic amine salts, aromatic amine adducts and aromatic amine salts.Amine and anhydride curing agents are being preferred to give lowviscosity and room temperature cure.

Typically the pre-preg resin, infusion resin and surface resin materialshave a different viscosity. The viscosity of the pre-preg resin isusually selected to be higher than that of the surface resin at roomtemperature (20° C.). The surface resin typically has a higher viscositythan the pre-preg resin when heated to keep the surface resin close tothe mould surface during processing.

The ratio of the viscosity, measured at 20° C. ambient temperature, ofthe pre-preg resin material and of the surface resin material istypically from 2 to 14/1, more preferably from 4 to 12/1. The surfaceresin material preferably has a higher viscosity than that of thepre-preg resin material if the assembly is heated prior to or duringcuring. The ratio of the viscosity, during such heating, of the surfaceresin material and of the pre-preg resin material may be from 5 to 25/1,more preferably from 10 to 15/1.

The pre-preg resin is preferably selected from the group consisting ofthermoset resins such as epoxy, cyanate ester and phenolic systems.Suitable epoxy resins include diglycidyl ethers of bisphenol A,diglycidyl ethers of bisphenol F, epoxy novolac resins and N-glycidylethers, glycidyl esters, aliphatic and cycloaliphatic glycidyl ethers,glycidyl ethers of aminophenols, glycidyl ethers of any substitutedphenols and blends thereof. Also included are modified blends of theaforementioned theiniosetting polymers. These polymers are typicallymodified by rubber or thermoplastic addition. Any suitable catalyst maybe used. The catalyst will be selected to correspond to the resin used.One suitable catalyst for use with an epoxy resin is a dicyandiamidecuring agent. The catalyst may be accelerated. Where a dicyandiamidecatalyst is used, a substituted urea may be used as an accelerator.Suitable accelerators include Diuron, Monuron, Fenuron, Chlortoluron,his-urea of toluenedlisocyanate and other substituted homologues. Theepoxy curing agent may be selected from Dapsone (DDS), Diamino-diphenylmethane (DDM), BF3-amine complex, substituted imidazoles, acceleratedanhydrides, metaphenylene diamine, diaminodiphenylether, aromaticpolyetheramines, aliphatic amine adducts, aliphatic amine salts,aromatic amine adducts and aromatic amine salts.

The fibres of the pre-preg layer may be comprised of fibrous materialsuch as glass fibre, aramid, carbon fibre, or natural fibres such asjute or hemp.

The pre-preg resin material may be a they epoxy resins. The pre-pregresin material typically has a viscosity of from 0.75×10⁵ to 5×10⁶ Pa·smeasured at 20° C.

This pre-preg resin typically has a sufficiently high viscosity at roomtemperature to prevent it from significantly impregnating the structuraldry fibrous reinforcing material 102, 103 during the period, typicallyfrom 1 to 3 hours, of the resin infusion process during which thepre-preg resin is under vacuum. Preferably a pre-preg system such asWE90-1 or WE92 available from Gurit which have a viscosity of around1×10⁵ Pa. at 20° C. would be used.

The pre-preg resin is preferably formulated to be a thermosetting epoxyresin with a latent curing agent, which is activated by heat. Otherthermosetting resins may be used; such as those derived from cyanateester and phenolic systems. Suitable epoxy resins include diglycidylethers of bisphenol A, diglycidyl ethers of bisphenol F, epoxy novolacresins and N-glycidyl ethers, glycidyl esters, aliphatic andcycloaliphatic glycidyl ethers, glycidyl ethers of aminophenols,glycidyl ethers of any substituted phenols and blends thereof. Alsoincluded are modified blends of the aforementioned thermosettingpolymers. These polymers are typically modified by rubber orthermoplastic addition. Any suitable catalyst may be used. The catalystwill be selected to correspond to the resin used. One suitable catalystfor use with an epoxy resin is a dicyandiamide curing agent. Thecatalyst may be accelerated. Where a dicyandiamide catalyst is used, asubstituted urea may be used as an accelerator. Suitable acceleratorsinclude Diuron, Monuron, Fenuron, Chlortoluron, bis-urea oftoluenedlisocyanate and other substituted homologues. The epoxy curingagent may be selected from Dapsone (DDS), Diarnino-diphenyl methane(DDM), BF3-amine complex, substituted imidazoles, acceleratedanhydrides, metaphenylene diamine, diaminodiphenylether, aromaticpolyetheratnines, aliphatic amine adducts, aliphatic amine salts,aromatic amine adducts and aromatic amine salts.

The preferred embodiments of the present invention provide the use, forforming a composite laminate having a high quality smooth defect-freesurface that can be painted, of the combination of (a) a low temperatureactivated, typically from 50° C. and above, more typically from 50° C.to 90° C., relatively high viscosity thermoset curing resin for forminga surface of the composite laminate with (b) a relatively low viscositythermoset curing resin suitable for resin infusion processing forforming, after infusion into fibre-reinforcement located adjacent to thesurfacing resin, a fibre-reinforced structure of the composite laminate.

The surface resin film is easy to sand, if necessary, to prepare thelaminate surface for subsequent painting.

In accordance with the preferred embodiments of the present invention,the surface resin is formulated to provide the desired correctcharacteristics. In particular, the surface resin has a viscosity sothat it can be applied into a mould at about ambient temperature andexhibit the desired levels of tack to the mould and drape. Heat may besupplied to the resin to initiate or accelerate curing either during orafter completion of the resin infusion stage.

In higher production rate vacuum infusion production, the tooling isheated during or after resin injection to speed up the cure rate. Thisoffers the opportunity to mix and co-cure these different materials.This is typically a temperature of from 50-90° C. to enable the use oflower cost tooling. The target format is a low temperature (50° C.)activated catalytic cure.

The surfacing layer preferably contains surfacing resin and a polyesterveil. During manufacture of the material, the polyester veil is firstapplied to the top of the surface resin. Some pressure is then appliedto push the polyester veil into the top of the surface resin.Preferably, the polyester veil is located at a position within the upperportion of the surfacing resin layer, i.e. the polyester veil is coveredon both sides by a respective portion of the surfacing resin layer, witha larger portion, i.e. a majority, on one side that is to be locateddirectly adjacent to the mould surface. If a first fibre layer is alsointegrated into the surfacing layer, and in particular into the surfaceof the surfacing layer that is to be located remote from the mouldsurface, also the fibre layer is pressed into the surface resin toensure that the surface material is maintained integral with, and staysfixed to, the fibre layer.

In the present invention it is preferred that the thickness of thesurface film resin is between 100 and 400 microns, more preferably from100 to 300 microns. Within this thickness range it has been found theresin can be made partially air permeable. Any air between the mouldsurface and the surface layer can pass through the surface layer andinto the more highly air permeable dry fibre layers, to then be drawnaway into the vacuum source.

The surfacing layer is structured and formulated so that the opposedsurfaces exhibit differential tack. There is relatively high tack on onesurface, the surface that is intended in use to contact and adhere tothe mould surface, and relatively low tack on the opposite surface, thesurface that is intended in use be manually handled and so is easier tohandle. This tack differential can be achieved by providing the scrimmaterial within the solid resin sheet, but offset relatively towards thelower tack surface. This means the tack of the material is moreconsistent and dependent only on the resin formulation of the surfaceresin which allows it to be formulated to give the desired andconsistent tack level. Furthermore, the high tack level can ensure thata high degree of wetting of the mould surface can be achieved, whichrenders the surfacing layer to be uniformly adhered to the mould surfaceover the entire surface area of the surfacing film. This in turnprevents reticulation of the surfacing layer from the mould surfacefollowing resin curing.

In addition, the surfacing material is tolerant to handling pressure, orthe pressure generated when the product is wound onto a roll. As aresult the surfacing material used in the method of the presentinvention has extended room temperature storage prior to use.

The fine polyester scrim within the surfacing resin layer serves twopurposes. It helps prevent fibres from the reinforcement entering thesurface resin layer. The fine weave layer also helps prevent the resinin the surface resin film layer reticulating off the tool surface givinga better quality of finish. The polyester scrim itself is easy to sandand does not result in abrasive particles damaging the surface. As wellas providing a thickness buffer to avoid fibre print the surface resinlayer provides a protective barrier for reducing moisture ingress intothe laminate. Glass fibre strands close to the surface can acceleratemoisture ingress by a wicking mechanism. The surface resin can betoughened and the modulus reduced which is a particular advantage asthis helps to prevent cracks from the mismatch in thermal expansionbetween the paint and the laminate. The tailored surface resin helpsimprove paint chipping that occurs in impact situations.

For composite structures requiring a painted finish, the preferredembodiments of the present invention can reduce the time taken and costto prepare a Vacuum Assisted Resin Transfer Moulding (VARTM) fibrereinforced composite component for painting, and moreover the finaldurability of the painted component can be improved. When using VARTMmethods to produce a fibre reinforced composite component, the preferredembodiments of the present invention, in order to produce a finish oncomposite part that would be easy to prepare for painting, can employ atemperature activated theanoset surface layer which can eliminate theneed to apply, and wait for, an in mould gelcoat to tack off during themanufacturing process, The preferred embodiments of the presentinvention can provide a toughened flexible interface between the paintand the composite part to improve the durability of the final paintfinish.

The manufacturing process of the preferred embodiments of the presentinvention combines hot-melt and infusion technologies to create adefect-free surface laminate ready for painting operations with superiormechanical properties due to the selected use of pre-preg materials. Asurface resin layer with a structural fibre reinforcement layer(hot-melt) is placed against the mould and a composite layout compatiblewith infusion technology is placed over it to provide a ventingstructure and allow entrapped air to pass out during processing. Therheological behaviours of the hot-melt and infusion resins aredifferent.

The preferred embodiments of the present invention can also provide asufficient tack level to retain the first dry reinforcement layer on thereleased tool surface. It is particularly suitable for large parts suchas wind turbines, bridges, and boat hulls.

This method of the preferred embodiments of the present invention isparticularly suitable for the production of wind-turbine aerofoilsections and any other large components with simpler curvature such asmarine craft, ray-domes, architectural mouldings and bridges usinginfusion technology.

The preferred embodiments of the present invention can provide themanufacture of a composite structure with a defect-free surface, whichis ready for painting. By avoiding the need for a gelcoat,correspondingly there is no need for any gelcoat handling, whichimproves the health and safety aspects of the manufacturing process. Inknown processes that employ a gelcoat layer, the gelcoat layer providesthe advantage that it provides tack to hold in a correct position on themould surface the first layer of fibre reinforcement The preferredembodiments of the present invention provide the tack in the absence ofsuch a gelcoat layer, because the surfacing layer provides the requiredtack for the first layer of reinforcement so that it can be can becorrectly positioned into the mould.

The preferred embodiments of the present invention can reduce the totalproduction time and the amount of manual labour required for themanufacturing cycle.

Also, in this manufacturing method of the preferred embodiments of thepresent invention a good surface finish is obtained without the need foradditional tissues and high cost fine weave fabrics as compared to someknown processes. This can enable lower cost heavier weight reinforcementto be used as the first ply into the mould. The resulting surface freeof defects is the primary result which can yield a reduction in theoverall time and labour required for the production of a paintedcomposite surface.

The surface resin layer can also provide a protective barrier forreducing moisture ingress into the composite laminate structure. Thesurface resin can also act as a buffer, and its increased toughnesshelps to reduce inadvertent paint chipping that can occur in impactsituations when the composite product is in operation.

In known resin infusion processes, unidirectional (UD) fibrereinforcement materials that are subject to the resin infusion may bestitched or bonded into a fabric format to give a handleable fibre toput into the mould. However, this expedient adds manufacturing cost andlowers the properties of the resultant composite laminate. Inembodiments of the present invention however, the use of aunidirectional (UD) pre-preg is cost effective, because the resin in thepre-preg maintains fibre alignment and can be made tougher and morefatigue resistant, and so the method can use the lowest cost fibrepre-cursors yet give high level properties in the resultant compositelaminate. For example, in order to manufacture a turbine blade shell, inaccordance with one embodiment of the present invention,pre-consolidated pre-preg UD stacks are interleaved with dry off-axisfabric reinforcements. The dry reinforcements are then infused withliquid resin. The combination of heating the mould and the exothermicreaction of the liquid resin is sufficient to raise the heat of thelaminate to activate the cure of the resin in the pre-preg UD material.This UD material then is thick and reactive enough to generate furtherheat through an exothermic cure to rapidly cure without the need forhigh heat input. This provides the technical advantage that lower cost,lower temperature resistant moulds and tools can be utilised to cure thecomposite laminate parts.

The present invention is further illustrated with reference to thefollowing non-limiting Example.

EXAMPLE 1

A laminate representing the tip section of a wind turbine blade wasfirst assembled onto a mould.

The laminate consisted of:

2 plies XE600 dry +/−45 stitched biax fabric2 plies of Gurit WE90-1\EGL1200\32% pre-preg1 ply XE600 dry +/−45 stitched biax fabric2 plies of Gurit WE90-1\EGL1200\32% pre-preg2 plies XE600 dry +/−45 stitched biax fabric

The unidirectional pre-preg material was set to be narrower at 400 mmwide than the biaxial fabric to simulate the typical construction of astructural shell. A peel ply and an infusion mesh were then applied tothe stack and resin feed pipes and vacuum lines set-up so to flow theinfusion resin in a transverse direction to the unidirectional fibre toensure flow into the interleaved biax material.

Gurit Prime 20LV+Slow hardener infusion resin was infused into thelaminate at 20° C. On completing the impregnation of the dry fibre thetemperature of the tool was increased to 90° C. and held for 6 hours.The infusion resin successfully impregnated all the dry fibre of thebiax fabric layers and both the infusion resin and the pre-preg resinco-cured together. An excellent adhesion was found between thematerials.

The present invention is not limited to the foregoing illustratedembodiments. It will be apparent to those skilled in the art thatvarious modifications to the present invention may be made withoutdeparting from the scope of the present invention as defined in theappended claims.

1. A method of manufacturing a fibre-reinforced composite moulding, themethod comprising the steps of: disposing at least one layer of fibrousreinforcing material within a mould; disposing at least one pre-preglayer adjacent to the fibrous reinforcing material, the pre-preg layercomprising fibrous reinforcement at least partially impregnated withuncured first resin material, to form a laminar assembly of the at leastone layer of fibrous reinforcing material and the at least one pre-preglayer within the mould; applying a vacuum to the assembly; infusing aflowable uncured second resin material, under the vacuum, into the atleast one layer of fibrous reinforcing material; and curing the firstand second resin materials at least partially simultaneously to form thefibre-reinforced composite moulding which comprises at least one firststructural portion formed from the fibrous reinforcement and the curedfirst resin material bonded to at least one second structural portionformed from the at least one layer of fibrous reinforcing material andthe cured second resin material. 2-7. (canceled)
 8. A method accordingto claim 1 wherein in the pre-preg layer the fibrous reinforcement isfully impregnated with uncured first resin material.
 9. A methodaccording to claim 8 wherein the pre-preg layer comprises apre-consolidated slab of a plurality of layers of fibrous reinforcementfully impregnated with uncured first resin material.
 10. A methodaccording to claim 1 wherein the at least one pre-preg layer ispartially impregnated and comprises a sandwich structure of a pair offibrous reinforcement layers on opposed sides of a layer of the uncuredfirst resin material.
 11. A method according to claim 1 wherein thelaminar assembly comprises a plurality of the layers of fibrousreinforcing material interleaved with a plurality of the pre-preglayers.
 12. A method according to claim 1 wherein the mould has a lengthand a width and the layers of fibrous reinforcing material and pre-pregextend substantially continuously along the length of the mould.
 13. Amethod according to claim 1 further comprising the step, before step(a), of disposing a surfacing layer on the mould surface, the surfacinglayer comprising a third uncured resin material and being in the form ofat least one solid sheet, and in steps (a) and (b) the laminar assemblyof the at least one layer of fibrous reinforcing material and the atleast one pre-preg layer is disposed over the surfacing layer within themould, and in the curing step (e) the third resin material is cured atleast partially simultaneously with the first and second resinmaterials.
 14. A method according to claim 13 wherein the surfacinglayer comprises a plurality of surfacing layer segments assembledtogether to form a continuous surfacing layer.
 15. A method according toclaim 14 wherein each surfacing layer segment has at least one edgethereof that partially overlaps an adjacent surfacing layer segment.16-34. (canceled)
 35. A fibre-reinforced composite moulding comprising astructural laminated portion being formed from at least one first layer,the first layer being formed from a pre-preg and comprising fibrousreinforcement and cured first resin material, laminated with at leastone second layer, the second layer comprising fibrous reinforcingmaterial and a cured second resin material, wherein the first and secondresin materials are mutually bonded by having been cured at leastpartially simultaneously. 36-38. (canceled)
 39. A fibre-reinforcedcomposite moulding according to claim 35 further comprising a surfaceportion laminated to the structural portion, the surface portion beingformed of a surfacing layer comprising a plurality of surfacing layersegments moulded together to form a continuous surfacing layer, thesurfacing layer comprising a third cured resin material supported on acarrier of a sheet material,
 40. A fibre-reinforced composite mouldingaccording to claim 39, wherein the sheet material of the surfacing layeris located nearer to an interface between the surface portion and thestructural portion than to an opposite exposed surface of the surfaceportion.
 41. A fibre-reinforced composite moulding according to claim35, which is a wind turbine blade.